F-1 (nuclear reactor)

Six in the evening, 25 December 1946

On 25 December 1946, at Laboratory No. 2 of the Soviet Academy of Sciences in Moscow, the team led by Igor Kurchatov completed the F-1 uranium-graphite reactor and brought it to criticality.

The last graphite layer went in at 2 p.m. Nonessential personnel then left, Kurchatov operated the cadmium control rods himself, and the reactor became critical at 6 p.m.

Before shutting it down late that night, he briefly raised its output to 100 watts.

45 tonnes of uranium, 400 of graphite

F-1 — the name meant simply 'Physical First' — was a natural-uranium, graphite-moderated pile containing 45 tonnes of uranium and 400 tonnes of graphite. I. S. Panasyuk, E. N. Babulevich, B. G. Dubovsky and A. K. Kondratiev were among the startup team.

It produced a controlled, self-sustaining uranium-fission chain reaction: the first achieved by a reactor in Europe and Asia. It was not the world's first — Chicago Pile-1 had done it on 2 December 1942.

Not a power station

F-1 was an experimental research pile, not a commercial electricity plant. The Soviet atomic project needed it to test reactor calculations and material purity and to supply operating knowledge.

The experiment confirmed that the project could build a more powerful industrial reactor to produce plutonium for a weapon; the first such reactor began operating in 1948.

When Lavrentiy Beria visited days later, moving needles and clicking instruments reportedly disappointed him, because it looked as though nothing had happened.